Many eruptions cool the atmosphere because of the aerosols they spew into the upper atmosphere. Aerosols that then reflect incoming light back out into space. The Pinatubo eruption was a famous cooler.

Love that image, from the compensating subsidence around the plume that's clearing clouds to the cap cloud at the top of the plume.

Volcano eruptions cool the planet mainly due to the sulfur dioxide and particles that are blown into the upper atmosphere. A large eruption can cause a measurable drop all over the world. Krakatoa both affected the weather and caused brilliant red sunsets for almost a year after the eruption.

Awesome picture! The white center at the top of the mushroom, with plumes of ash coming out on 4 sides is the volcanic steam and moisure-laden lower atmosphere brought up into the cold stratosphere condensing out.

Cloud cover parted by heat and shockwaves from the eruption. In other photos, they captured the complete pyroclastic ground flow of 1,100 DEG ash spreading out 4,000 feet.